The present invention relates to a cable connecting structure for an electrical connector for connecting a cable including cable cores each having a core conductor and a core sheath to respective contacts of the electrical connector with exposed core conductors of the cable cores by peeling leading end of the cable, and more particularly to a connecting structure for connecting a cable to an electrical connector, which is able to restrain characteristic impedance which tends to be higher at exposed portions of cable cores with the result of reduction in variances of the characteristic impedance over the length of the cable including the exposed portions of cable cores of the cable, thereby improving its transmission efficiency.
With an electrical connector for a cable including cable cores each having a core conductor and a core sheath, in general, the leading end of the cable is peeled to expose the core conductors of the cable cores, and the exposed core conductors are connected to contacts of the electrical connector.
Matching of characteristic impedance is generally required over the length of a cable as a transmission passage with a view to obtaining improvement in transmission efficiency and the like. If the transmission passage includes portions poor in matching of characteristic impedance, problems would tend to arise such as reduction in transmission efficiency and occurrence of noise due to reflection of signals at the portions.
In order to connect a cable to an electrical connector, however, it is needed to expose conductors of cable cores of the cable by peeling its leading end. Therefore, the exposed portions of the cable cores, in more detail, the exposed portions of both the core conductors and core sheaths exhibit inevitably lower dielectric constants εr than those of the remaining portions of the cable not being peeled or exposed, with the result that the characteristic impedances of the exposed portions tend to become higher.
A prior art proposal has attempted to lower the characteristic impedance ZO of the exposed portions. In the proposal, after the exposed portions connected to contacts of an electrical connector have been set in a metal die, the die is filled with molten resin which is then solidified, whereby the exposed portions are embedded in the solidified resin.
Even with this prior art proposal, it is difficult to achieve substantially same value of the characteristic impedance over the length of a cable owing to the fact that the characteristic impedance ZO of the exposed portions becomes higher to an excessive extent due to the high dielectric constant εr of the solidified resin. Moreover, the operation for solidifying the molten resin is time-consuming and the metal die used for covering the exposed portions by the resin increases the manufacturing cost. Therefore, this prior art proposal is not preferable in view of its efficiency and cost.
Accordingly, there is a need for a convenient method for reducing the characteristic impedance ZO of the exposed portions of cable cores to the desired value.